 On the shortest spanning subtree of a graph and the traveling salesman problem by Joseph Bernard Kruskal

By Joseph Bernard Kruskal, printed as Joseph B. Kruskal, Jr. Published in Proceedings of the American Mathematical Society 7(1), 48–50, February 1956. Received 11 April 1955.

Official article: www.ams.org/journals/proc/1956-007-01/S0002-9939-1956-0078686-7/S0002-9939-1956-0078686-7.pdf

Institutional scan: langevin.univ-tln.fr/cours/graphe/bonus/Krukskal.pdf

Cited passages: printed pp. 48–50, especially Construction A on p. 49 and the exchange argument on p. 50.